Increase run_slave control over shutdown process.
Increase run_slave control over shutdown process.

This has the latest round of fixes:
- Ensure the slave doesn't run 2 IssueReboot() calls back-to-back.
- Override the Twisted default SIGTERM handler with our own.
- Send log messages to the twistd.log file.

R=nsylvain@chromium.org


Review URL: https://chromiumcodereview.appspot.com/10837239

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@152579 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build